Synchronous sensing of inductor current in a buck converter control circuit

摘要

A sense resistor is placed in series with an output capacitor of a buck converter. The buck converter operates in a discontinuous mode such that there is a dead time in each switching cycle. A control circuit senses a voltage across the sense resistor and thereby generates a first signal I_CS. The control circuit detects an offset voltage in I_CS, where the offset voltage is the voltage of I_CS during the dead time in a first switching cycle. The control circuit level shifts the entire I_CS by the offset voltage, thereby generating a second signal I_CLS. I_CLS has the same waveform as the waveform of the inductor current. In a second cycle, I_CLS is used to determine when to turn off the main switch and when the start of the dead time occurs. I_CLS and the offset voltage are used together to determine when to turn the main switch on.